In the operation of boat motors such as outboard motors mounted on the backboard of a boat or the pivoted power unit of an inboard-outboard boat, mechanism that supports the motor to the boat carries a vertical axis about which the motor assembly or the power unit itself rotates. In steering the boat a rudder is not used. In place of the rudder, the entire motor assembly is turned and with it, of course, the propeller shaft is turned so that the slip stream is directed to the stern of the boat at an angle to the axis of the boat, causing the stern to be forced in one direction or the other across the axis, thereby rotating the boat and heading the bow in a desired direction.
Physically rotating the motor assembly is arduous, especially with larger size motors, and this invention is adapted to provide an assisting torque to rotate the motor assembly by using the slip stream of the propeller to exert a force on a small rudder positioned to the rear of the propeller.